Actuatable occupant restraining systems for use in vehicles are known in the art. Modern actuatable restraining systems often include a plurality of sensors, such as accelerometers, and an electronic control unit (“ECU”) that monitors the sensors. The ECU makes a determination, based on the signals from the sensors, if the restraining system should be actuated (e.g., a seat belt pretensioner activated, an airbag deployed, etc.). In early actuatable restraining systems, mechanical sensor switches were used for deployment control. Later, other types of crash sensor were used such as accelerometers. The simplest example of such a restraining system using an accelerometer used the accelerometer for measuring crash acceleration as a function of time. A controller monitored the output signal of the accelerometer and determined if the crash acceleration as a function of time was greater than a predetermined value, and, if so, the restraint was actuated.
Occupant actuatable restraining systems including their sensor arrangements and discrimination algorithms have become more complex in an attempt to better discriminate between, what is referred to as, deployment and non-deployment vehicle crash events. In particular, systems have been developed to “catch” certain vehicle events, e.g., high speed non-deformable barrier crash, for which it is desired to actuate the restraint system (i.e., a deployment crash event) and to “filter out” or “not catch” other vehicle events, e.g., undercarriage snag, for which it is not desired to actuate the restraint system (i.e., a non-deployment crash event”). Complicating the issue further is that such determination schemes are vehicle platform dependent. What may work to catch or filter out certain vehicle events on one particular vehicle platform may not work on another vehicle platform. It should also be noted that vehicle events, whether deployment or non-deployment events, are all referred to herein as “vehicle crash events”, even though the event may not be a “crash” as may be commonly understood. For example, an undercarriage snag is referred to as a non-deployment vehicle crash event even though an undercarriage snag is not considered a crash in its normal meaning.
Several patents have been issued describing methods and apparatuses for discriminating between deployment and non-deployment crash events. For example, U.S. Pat. No. 6,776,435 to Foo et al., assigned to TRW Inc., discloses a method and apparatus for controlling an actuatable restraining device using switched thresholds based on use of a crush zone sensor. U.S. Pat. No. 7,359,781 to Foo et al., assigned to TRW Automotive U.S. LLC, discloses a method and apparatus for determining symmetric and asymmetric crash events with improved misuse margins. U.S. Pat. No. 7,625,006 to Foo et al., assigned to TRW Automotive U.S. LLC, discloses a method and apparatus for controlling an actuatable restraining device using crush zone sensors for a safing function. U.S. Pat. No. 8,118,130 to Foo et al., assigned to TRW Automotive U.S. LLC, discloses a method and apparatus for controlling an actuatable restraining device using XY crush zone satellite accelerometers, i.e., multi-axis sensors. The teachings of each of these Foo et al. patents are hereby incorporated herein in their entirety.